PROJECT SUMMARY The overall goal of Project 5 is to provide engineering research (non-biomedical) for the remediation of sites containing typical airborne PCB congeners that may expose humans. Specifically, it is to determine whether plants can provide in situ phytoremediation of lesser-chlorinated PCB congeners from soil and groundwater sources like the municipal wastewater lagoon at Altavista, Virginia. Thus, the Project focuses on PCB congeners of higher volatility, which comprise significant mass, toxicity and persistence in the environment. Plants can uptake PCB congeners from soil and sediments, intercept semi-volatile congeners from the air onto the waxy cuticle of leaves and bark, and metabolize contaminants within plant tissues. In addition, plants can stimulate rhizosphere bioremediaton of PCBs by providing the habitat, redox potential, and substrates necessary for microbial biodegradation in the root zone. The significance of this project is to provide the scientific and engineering basis for development of land management strategies that can be used to intervene and clean PCB-contaminated sites. Four specific aims comprise Project 5: Aim #1. Identify plant metabolites of selected PCB congeners (PCB 11, 52, 77, 101, 126, 153) that are semi- volatile, persistent, and toxic; and also the uptake/selectivity/metabolism of chiral compounds (PCB 91 and 95). Aim #2. Elucidate the regulation of metabolism of PCBs by poplar plants (Populus trichocarpa) at the epigenetic and transcriptional levels. Aim #3. Identify microorganisms and functional genes associated with PCB dechlorination in enrichment cultures derived from PCB-contaminated soil and in un-enriched PCB-contaminated sediment. Aim #4. Characterize PCB-induced changes by plants and their associated rhizosphere microorganisms at a contaminated site (Altavista, Virginia) and in contaminated sediments using gene sequencing and transcriptomic responses. Our leading themes are to identify plant metabolites and microbial dechlorination processes in rhizosphere soils and sediments. We strive to understand the biochemical mechanisms necessary for full-scale phytoremediation of PCBs and the subsequent reduction of exposure at contaminated sites.